Coke is utter junk, of course, but it can be terribly refreshing. I probably drink a Diet Coke every other week. My "brand loyalty" is literally unquestioned – it never occurs to me to buy any other cola, not that there ever seems much of an opportunity to do so. Pepsi has a 9.5% share in the UK soft drinks market, far less than the 17% for Coke and even the 9.9% for Diet Coke. Diet Pepsi lags with a pitiful 5.3%.On the few occasions I have bought another cola (even that word looks alien and amputated), I've never been impressed. Fentiman's Curiosity Cola tastes flat and monotone, with a lingering undercurrent that reminds me of diesel. One ethically minded food and drinks company is launching a new cola in time for the Olympics. But a lifetime of conditioning and marketing can often make these products taste less like "the real thing" even though they may derive more of their flavour from genuine kola nuts.

It's a brave company that seeks to rival Coca-Cola. The drink has a presence in over 200 countries: "more than the UN itself", as one of its executives boasts. It's been the most valuable brand in the world for years. This is all a long way from its origins in the 1880s, when a morphine-addicted veteran of the American civil war concocted a cocaine and caffeine tonic which he claimed cured headaches, impotence and, handily, morphine addiction. After a certain amount of internal wrangling, a man named Asa Candler wound up with the rights to sell the drink, and made a vast fortune from it. He marketed Coca-Cola with a ferocity never seen before, and his commercial heirs have always followed his lead.

Coke is now the market leader in almost every country in the world, but rivals jostle with it across its markets. Pepsi outsells it in parts of Canada, the Caribbean, the Middle East and in Pakistan, whose cricket team is sponsored by Pepsi. Other rivals around the world are called things like Zam Zam Cola, Parsi Cola, Mecca Cola, Big Cola and the Indian Thums Up. On Madeira in the eastern Atlantic, a Fanta variant called Laranjada outsells it, and the Scots used to drink more Irn-Bru. Barr's lost its lead there in 2005, but throughout my childhood I lived in a dissident soda market.

However sketchy its ethics, Coke is a masterclass in the power of marketing and an unanswerable witness to America's cultural hegemony during the last century. But the company relies increasingly on other brands in its portfolio, and many Americans and Europeans are drinking less of the main product. Are you among them?